Delayed thrombocytopenia after treatment with abciximab: a distinct clinical entity associated with the immune response to the drug

Background: Acute thrombocytopenia is a recognized side-effect of treatment with the fibrinogen receptor antagonist, abciximab, a chimeric (human/mouse) Fab fragment. The etiology of this complication is riot fully understood. Generally, abciximab-induced thrombocytopenia occurs within a few hours of starting treatment with the drug. We have characterized a group of 13 patients who first developed thrombocytopenia 3-6 days after abciximab was discontinued. Objective: To characterize clinical and serological aspects of this newly recognized clinical entity. Patients and methods: Clinical information was obtained from attending physicians and review or hospital records. Antibodies reactive with abciximab-coated platelets were characterized by flow cytometry. Results: In each patient, IgG and/or IgM antibodies reactive with abciximab-coated platelets were identified. These antibodies Could be distinguished from similar antibodies present in many normal persons by two criteria-they were relatively resistant to inhibition by normal Fab fragments, and they reacted preferentially with platelets coated with 7E3. the murine monoclonal antibody from which peptide sequences in abciximab are derived. Antibodies with these characteristics were not found in pretreatment serum from three of the thrombocytopenic patients or in patients given abciximab who did not develop thrombocytopenia. Conclusions: Delayed thrombocytopenia' after treatment with abciximab is Caused by antibodies produced in response to the drug. These antibodies may be specific for murine peptide sequences in abciximab but could recognize other target epitopes on abciximab Physicians administering-coated platelets. abciximab should be aware of this potential complication of treatment, which usually occurs after discharge from hospital.